Field of the Invention
The present invention relates to a method of controlling an articulated robot including a plurality of motors which drive joints connecting links respectively, and a plurality of detection devices which detect rotation amounts of the joints connecting the links respectively.
Description of the Related Art
An articulated robot, in which both ends of respective links are connected by rotary joints whereby the links are able to perform a bending movement, has been widely used. In the articulated robot, as some of the links have torsional joints which rotate in a torsional direction within a cross-section vertical to a longitudinal direction of the link, the articulated robot is able to perform complicated movement such as six-axis motion or seven-axis motion similar to that of a human arm.
An articulated robot may interfere with another object in any situations including test operation, teaching, and actual operation. When an articulated robot interferes with another object, there is a possibility that an overload is caused in a particular joint so that an origin is shifted, or that a damage is caused in a part such as a reduction gear, a bearing, or the like constituting the joint. If an articulated robot is operated in a state where an origin is shifted in a joint or a part of a joint is damaged, a work may be dropped due to deterioration in the operation accuracy, power consumption may increase, or another articulated robot may be interfered. As such, during operation of the articulated robot, it is required to early find an abnormality in operation in a plurality of joints and to take necessary measures such as part replacement, readjustment, and the like.
In a robot system disclosed in Japanese Patent Application Laid-Open No. 11-202914, a control device takes in load information (electric current) of a motor provided for each of the joints of an articulated robot, and an output of an encoder provided for each of the motors, and computes a current load state of each joint in real time. Then, when a load exceeding an allowable range is computed for any of the joints, the control device terminates the articulated robot and gives notification of the joint in which the load exceeding the allowable range is caused.
In the robot system of Japanese Patent Application Laid-Open No. 11-202914, it is impossible to accurately determine a load state of each of the joints of the articulated robot. For example, when an arm of the articulated robot interferes with another object, even though the electric current variations in the motors and the output variations of the encoders in two joints are the same, the maximum loads caused in the two joints differ largely. As a large difference is caused between the maximum loads placed on the two joints due to interference according to the rotational directions and the load states of the two joints before the interference, broken conditions of the parts cannot be determined accurately.